Remotely installed steam generator nozzle dam system

ABSTRACT

A system and method for installing a nozzle dam unit (26) in a nuclear steam generator having a head (12) including a head internal surface, a manway (14) penetrating the head, and a nozzle (16) penetrating the head. The system comprises a manipulator (76) adapted to be passed through the manway and having one end (82) adapted to be attached remotely to the head internal surface and a free end including a clamp member (104). A plurality of nozzle dam segments (54, 56, 58) are each sized to pass through the manway and carry means thereon (120) for engaging at least one other segment, the segments when fully engaged to each other forming a dam subassembly sized to pass into and seat against the nozzle. The manipulator is controlled so that the clamp member grasps and supports one of the dam segments within the head until the subassembly is formed within the head, and then is translated within the head until the dam subassembly seats within the nozzle.

BACKGROUND OF THE INVENTION

The present invention relates to the servicing of nuclear steamgenerators, and more particularly, to the installation of nozzle damsfor permitting servicing to proceed within the steam generator while thenuclear reactor core is being refueled or otherwise serviced.

A variety of manually installed nozzle dams have been used in nuclearpower plants, such as the type shown in U.S. Pat. No. 4,482,076, "NozzlePlug For Submersible Vessel", and U.S. Pat. No. 4,483,457 "Hinged SteamGenerator Nozzle Plug". These have proven effective in isolating thedrained steam generator lower head area from the water in the steamgenerator hot or cold leg during reactor refueling, and thus have savedconsiderable time in total plant outage. Nevertheless, the manualinstallation of these plugs requires that many "jumpers" sequentiallyenter and exit the steam generator due to the high radiation in thesteam generator head, even when drained.

The cost, duration of time, and exposure to radiation of the "jumpers"would be reduced considerably if the nozzle could be installed remotely.This is a difficult task, however, in that the nozzle dam components areheavy, and the space available in the head for maneuvering, is limited.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for installing a nozzle dam in a nuclear steam generator, withoutrequiring complete human entry into the steam generator.

This object is accomplished in accordance with the invention, by firstinstalling a manipulator component, such as a multi-axis robot arm, onthe tube sheet or other interior support of the steam generator, suchthat the robot end-effector or jaw has access to the manway and thenozzle in the steam generator head region. The manway diameter istypically smaller than that of the nozzle, so that the nozzle dam andassociated supporting structure are manually passed into the steamgenerator head in component parts and assembled using the manipulatorwithin the head or nozzle. The manipulator itself can be installed onthe steam generator tube sheet using a block and tackle from outside thesteam generator or by using the manipulator to install itself inconjunction with a support bar across the steam generator manway as asupport point. No human entry into the steam generator is required toinstall the manipulator or the dams, with the exception of arm entriesmade while passing items through the manway.

The main body of the dam is formed from a plurality of sections orsegments, typically three, the center section having a support bar whichis grasped by the manipulator jaw as the center section is passedthrough the manway. The grasped section of the dam is moved to the sideof the manway axis to permit a worker outside the manway to slideanother dam section onto an edge of the center section, as by a dovetailjoint. Spring loaded camlocks or the like prevent the pieces fromsliding apart once joined. This subassembly is then moved to theopposite side of the manway axis and another section installed on thegrasped section in a similar manner. A flexible seal is wrapped aroundone face and the circumferential rim of the completed assembly.

The dam assembly with the associated seal is then rotated and displacedas appropriate from the vicinity of the manway into engagement with theinner diameter of the nozzle.

Structural support members to hold the dam assembly against hydraulicpressure, for example support bars or the like for attachment to apermanent support ring on the steam generator walls around the nozzlepassage, may be installed sequentially by the manipulator as thesestructural components are passed through the manway after the assemblyis seated in the nozzle. Similarly, locking pins for securing the damassembly radially against the nozzle inner wall may be actuatedremotely.

Positioning of the manipulator, assembling and positioning of the dam,and installation of the support structure can be monitored remotelyusing T.V. cameras installed in the tube sheet and on the manipulator.If pneumatic or hydraulic actuation of locking pins or other structureassociated with the dams is required, supply lines can be provided onthe manipulator.

The dam unit is removed in the reverse order of the installation.

The system and method of the present invention considerably reduces theamount of radiation exposure to technicians associated with installingand removing a nozzle dam. A typical rule of thumb is that one man canreceive a limit of 2.25 Rem while performing tasks for a given plantoutage, and the typical radiation field in the steam generator headwould be in the range of 5-25 Rem per hour. For a two-loop plant (havingfour nozzles), and a radiation field of only 5 Rem per hour, the use ofthe present invention is estimated to require about three fewer menduring a given outage. In a four loop plant (eight nozzles) and aradiation field of 25 Rem per hour, the present invention is estimatedto require fifty fewer men.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will be moreevident from the following description of the preferred embodiment andaccompanying drawings in which:

FIG. 1 is a schematic representation of a portion of the lower head of anuclear steam generator with a single nozzle dam unit installed in thehot leg nozzle in accordance with the present invention;

FIG. 2 is a detailed view of the sealing arrangement between the nozzledam subassembly and the nozzle inner wall for the arrangement shown inFIG. 1;

FIG. 3 is an elevation view of the concave side of the nozzle damsubassembly of FIG. 1, which faces the steam generator;

FIG. 4 is a sectioned elevation view through line 4--4 FIG. 3;

FIG. 5 is a side elevation view in section of the nozzle dam unit ofFIG. 1;

FIG. 6 is an elevation view of the installed nozzle dam unit of FIG. 1,as viewed from the steam generator head;

FIG. 7 is a schematic view of one type of manipulator suitable forremotely installing the nozzle dam unit shown in FIGS. 5 and 6;

FIG. 8 is a schematic view of a portion of nuclear steam generator lowerhead after the manipulator has been installed on the tube sheet, and thecentral section of a nozzle dam has been passed through the manway andgrasped by the manipulator;

FIG. 9 shows a step subsequent to that represented in FIG. 8, whereby asecond section of the nozzle dam is manually connected to the centralsection, in the vicinity of the manway;

FIG. 10 is a schematic view of a step subsequent that represented inFIG. 9 wherein a third section the nozzle dam is secured to the centralsection in the vicinity of the manway;

FIG. 11 is a schematic view of the rotation of the dam subassembly inthe vicinity of the manway, preparatory to displacement toward thenozzle;

FIG. 12 is a schematic view of the position of the manipulator and thedam subassembly in the vicinity of the nozzle;

FIG. 13 is a schematic view of the position of the manipulator and thenozzle dam assembly prior to insertion into the nozzle;

FIG. 14 is a schematic view of the position of the manipulator and damas dam assembly as the latter is inserted into the nozzle;

FIG. 15 is a schematic view of the position of the manipulator and damassembly as the latter is seated in the nozzle;

FIG. 16 is a section view along line 16--16 of FIG. 9, showing thepreferred dovetail joint between the edges of adjacent nozzle damsection;

FIG. 17 is an elevation view of a spring loaded camlock that is suitablefor use in locking together the dam sections;

FIG. 18 is a schematic representation of the loop and hook arrangementfor securing the seal to the dam subassembly shown in FIG. 2;

FIG. 19 is a schematic view similar to FIG. 2, of another embodiment forsecuring the seal to the dam subassembly;

FIG. 20 is a schematic representation similar to FIG. 18, for theembodiment of FIG. 19;

FIG. 21 is a schematic of a suitable quick acting screw clamp to serveas a strut member between the dam assembly and the support structure inthe embodiment of FIGS. 5 and 6;

FIG. 22 is a schematic view of the concave side of a second embodimentof the dam subassembly;

FIG. 23 is a side view of the dam subassembly of FIG. 22;

FIG. 24 is a schematic of a suitable quick acting locking pin for use inradially securing the dam assembly or FIGS. 22 and 23, into the innerwall of a nozzle; and

FIG. 25 is a schematic representation of the complete system of thepreferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a portion of the lower head 12 of a nuclear steamgenerator, including a substantially circular manway 14 penetrationhaving a first diameter, and a circular or tapered nozzle 16 penetrationhaving a second, larger diameter. The nozzle is connected to a hot orcold leg pipe 18, which contains, during normal operation, a flow ofprimary coolant from the nuclear reactor vessel into the steamgenerator. The upper portion of the lower head is defined by a tubesheet 20, consisting of a thick horizontal plate into which are secureda multiplicity of tube ends 22, the tubes extending upwardly through thesteam generator. Some steam generators, such as the one shown in FIG. 1,also have a vertical support column 24 substantially centered in thelower head region.

During plant outages, it is often necessary to perform repair or otherinspection services on the tubes, and thus the steam generator must bedrained so that the servicing equipment can be passed through the manway14 for attachment to the tubes. This servicing can be performed inparallel with refueling or other servicing associated with the nuclearreactor core, only if the water in the refueling pool, which covers thenuclear core and often extends considerably above the elevation of thenozzle, can be isolated from the steam generator head.

This is accomplished by installing a nozzle dam unit 26 such as is shownin FIGS. 1 and 2, the typical unit consisting of three main parts. Thefirst is a dam subassembly 28, having a generally domed surface. Theconvex surface 30 faces the nuclear reactor, and the cylindricalperimeter 32 is nearly the same diameter as the cross section of thenozzle in the vicinity of the entry into the steam generator. The secondpart comprises a generally circular seal member 34 having one or morecircumferential, seal tubes 36 for engaging the inner wall 38 of thenozzle. Typically, these seals are inflatable. The third component is asupport structure 40 for the dam assembly, connected to a rigid portionof the steam generator such as the inner surface 42 of the head, or, inan alternative embodiment, connected directly to openings in the innerwall of the nozzle itself. These types of dam units are more fullydescribed in U.S. Pat. Nos. 4,482,076 and 4,483,457, the disclosures ofwhich are hereby incorporated by reference.

FIG. 2 shows the details of the interface between the nozzle wall 38 andthe seal 34. Typically, the seal has a substantially circular solidportion 44 covering the convex surface 30 of the dam subassembly, and arim portion 46 resting on the substantially cylindrical surface 32 ofthe dam subassembly. A supply line 48 for compressed air is provided forexpanding the one or more inflatable seal tubes 36 against the nozzlewall. If desired, the steam generator side of the dam subassembly rimcan include a circular flange 50 for trapping a circular trailing edge126 of the seal 34 in interference engagement between the flange and thenozzle inner wall.

Conventionally, the dam unit 26 is installed entirely, or substantiallyentirely, by human entry through the manway 14 and the sequentialpassage into the manway and head region 12 of dam segments which areassembled by the technician in the nozzle region, while the techniciankneels in the head region. In accordance with the present invention, anozzle dam unit can be completely installed and removed remotely, i.e.,without the need for a human to enter the steam generator head region.

FIG. 3 shows schematically a nozzle dam subassembly 28 from the concaveside 52, which consists of, in this instance, three separate segments54, 56 and 58, each of which is small enough to pass through the manway14, but which when assembled, form a bowl, or dome shaped plug or damsubassembly 28 having a diameter substantially equal to that of thenozzle at a preselected portion thereof.

FIG. 4 is a section view along lines 4--4 of FIG. 3 and shows that eachof the segments 54, 56, 58 is somewhat cup-shaped when viewed insection, some of the walls 60, 62 of the cup formed by ribs or webb-likemembers projecting from the concave surface of the segments.

FIG. 5 shows schematically a first embodiment of a nozzle dam unit 28that can be installed remotely wherein the dam support structure 40 isadapted to seat against a bolt ring 64 that is a permanent part of theinner surface 42 of the head immediately surrounding the nozzle opening66. The support structure includes a plurality of support bars 68, 70oriented transversely to the nozzle axis 74, and a plurality of struts72 or 72' which are substantially parallel to the nozzle axis. The strutmay either be adjustable, as shown ar 72, or fixed length, as shown at72'. The struts transmit the substantially axial force imposed on thedam subassembly 28, to the support bars 68, 70, which in turn load thebolt ring 64 in tension and keep the dam subassembly 28 in positionThus, the seal shown in FIG. 2 does not play a role in resisting thehydraulic load on the dam subassembly, but merely provides a fluid seal.

To accomplish the objectives of the present invention, a manipulator 76,preferably the type shown in FIG. 7, is passed through the manway 14 andmounted at one end 78 in the steam generator head 12, leaving a free end80 for performing the operations necessary to grasp the components ofthe nozzle dam unit at the manway 14, and assemble the components into anozzle dam unit in the nozzle 16. The manipulator shown in FIG. 7 isavailable from Schilling Development, Inc., of Davis, Calif., and isidentified as Titan 7F. The manipulator has seven degrees of motion, asfollows:

(a) a base rotary actuator 82,

(b) a first pivot joint 84 for the upper arm 86,

(c) a second pivot joint 88 for the forearm 90,

(d) a pitch and yaw assembly 92, and

(e) a jaw assembly 94 or a similar clamping or grasping end effector andwrist rotator.

An associated servomechanism and electronics package 96, and masterconsole 100 with cables is also provided commercially by the vendor. Thevendor also provides hydraulic and inductive couplings as part of thejaw assembly.

The manipulator shown in FIG. 7 is preferably installed in the steamgenerator lower head in the configuration shown in FIG. 8. The base end82 of the manipulator 76 can be fitted to a pedestal support structure102 that is adapted to engage a plurality of tube ends 22 in the tubesheet 20, and thus rigidly support the base end 82. The connection ofthe pedestal 102 and base end 82 to the tube sheet 20 can be performedremotely by use of a block and tackle arrangement (not shown) or by a"bootstrap" technique whereby the manipulator 76 is inserted through themanway 14 and a bootstrap bar is secured relative to the manway. The jaw104 is actuated to grasp the bootstrap bar and the manipulator iscontrolled so that the base end 82 moves relative to the stationary jawand bootstrap bar, until the pedestal 102 is positioned over theselected tubes, and the base is locked in place. This locking can beachieved in a manner such as is shown in U.S. Pat. No. 4,018,346, whichrepresents one of the variety of known techniques for locking servicingequipment into the tubes of a tube sheet. Another technique is tosupport the manipulator at least in part on the center column 24 shownin FIG. 1, where available.

FIGS. 8-15 show the preferred sequence of operation of the manipulator76 by the technicians who stand outside the manway 14, in order toremotely install the type of nozzle dam unit 26 shown in FIGS. 5 and 6.In this embodiment, the dam subassembly 28 has three segments althoughthe invention can be implemented with a dam subassembly having two ormore segments.

In FIG. 8, the first, central segment 56 is inserted through the manway14 with the convex side 30 visible. The convex side includes a controlbar 106 which is grasped by the free end 80 of the manipulator as shown.The bar is preferably at the center of gravity of the center segment 56,and this center should also be identical to the center of gravity of thedam subassembly 28 shown in FIG. 3.

In FIG. 9, the manipulator has lifted the center segment 56 vertically,to one side of the axis 108 of the manway, such that a second segment 54can be inserted into the head through the manway. The first and secondsegments have longitudinal edges 110, 112 which, in FIG. 9, aresubstantially parallel to the manway axis 108. These edges haverespective male and female formations which permit a sliding,interference engagement between the segments 54, 56 which is effectuatedas the technician advances the second segment through the manway. Onesuitable arrangement of the male and female formations 114, 116, isshown in FIG. 16. This arrangement is, in effect, a dovetailrelationship extending over the full length of the mating edges 110,112.

When the first and second segments 56, 54 have been joined and are inproper registry, four locking bolts 118 carried by one or the othersegment are actuated to lock the two segments together One such bolt 118is illustrated in FIG. 17, and is more fully described in U.S. Pat. No.4,744,392, "Nozzle Dam Segment Bolt and Keeper", the disclosure of whichis hereby incorporated by reference. Although the bolt shown in FIG. 17can be actuated in some instances by the technician's reaching throughthe manway, the bolts are preferably fitted with hydraulic or pneumaticactuators which can be controlled through pneumatic or hydraulic linesand connections associated with the manipulator and an external controlsystems (See FIG. 25).

FIG. 10 shows that after the first 56 and second 54 segments have beenlocked together, the manipulator 76 is controlled so that the centersegment 56 and connected second segment are lowered to the other side ofthe manway axis 108. The center segment 56 has another longitudinal edge120 parallel to the manway axis, for mating with a longitudinal edge 122on the third segment 58, which is passed through the manway and lockedto the first segment 56 in the same manner as was described with respectto FIG. 9. As will be described more fully below, the seal member 34 isthen secured to the subassembly 28 to form the dam assembly 124.

As shown in FIGS. 11 and 12, the manipulator 76 is then controlled todisplace the completely formed dam assembly 124 from the vicinity of themanway 14 to the vicinity of the nozzle 16, in a manner which has theeffect of rotating the assembly 180° as viewed in the drawings, so thatthe convex side 30 carrying the seal face 44 is visible. The manipulatorforearm 90 and wrist 92 are further controlled as shown in FIGS. 13 and14 until the convex side 30 of the assembly 124 is positioned in theopening 66 of the nozzle whereupon the assembly 124 is advanced alongthe nozzle axis 74 to the seated position shown in FIG. 15.

It should be appreciated that preferably, the seal member 34 should besubstantially in place on the dam assembly before the assembly istransported from the position shown in FIG. 11 to the position shown inFIG. 15. FIG. 12 shows a front view of the dam assembly, on the domeside, with the circular portion 44 of the seal facing the viewer.Preferably, the seal member 34 is secured to the third segment 58 andfolded thereon into a ball or the like with Velcro straps or similarbinding before the third segment is passed through the manway as shownin FIG. 10. When the dam subassembly 28 is fully formed as shown in FIG.11, the straps are manually released with a pull and the seal opensfully.

As shown in FIGS. 2 and 18, the trailing edge 126 of the seal may have aplurality of stainless steel loops 128 extending therefrom and theflange 50 or trailing surface of each segment has a hook 130 or the likesuch that the technician can, while the subassembly is in the positionshown in FIG. 11, pull the loops 128 over the corresponding hooks 130 ata plurality of locations, thereby properly fitting the seal member 34 onthe dam subassembly 28.

Alternatively, as shown in FIGS. 19 and 20, the base of the rim portionof the inflatable seals can have a plurality of tab extensions 132 whichfit through respective openings 134 in the flanged portions of the damsubassembly and the technician can slide a locking pin 136 through ahole in each tab extension.

With the seal in place while the dam assembly is in position shown inFIG. 11, the subsequent control of the manipulator to the position shownin FIG. 15 results in substantially circumferential contact of theflexible, tubular seals 36 with at least some of the nozzle inner wall38, i.e., within the nozzle.

The manipulator jaw 104 is then released from the control bar 106 andreturned to the manway 14 where the technician sequentially feeds thejaw with, for example, four dam support bars 68, 70 which are attachedto the bolt ring 64 in, for example, the relationship shown in FIGS. 5and 6. Each support bar preferably carries a pair of adjustable strutmembers 72 at the locations indicated at 138, for the purpose oftransmitting the hydraulic loads from the dam assembly 124 to the boltring 64. The support bars 68, 70 can be secured to the bolt ring bymeans of respective key ways 140 and key bolts 142.

The strut members 72 can take a variety of forms, one of which is shownin FIG. 21. This is a quick acting screw clamp available from the CarrLane Manufacturing Co., St. Louis, Mo. under the name Barlock. Thisclamp has a sleeve 144 that is mounted in the support bar 68 or 70, anda screw portion 146 adapted to permit rapid linear advance of the screwthrough the sleeve until the foot 148 contacts the dam assembly 124,whereupon a twist of the handle 150 tightens the screw 146 to take upany clearances and produce a rigid overall nozzle dam unit 26. If anon-adjustable strut 72' is employed, a groove at the leading end of thestrut fits over two adjacent walls 62 and wall 60.

The present invention can be implemented with other types of nozzle damunits, such as described in U.S. Pat. No. 4,482,076, "Nozzle Plug ForSubmersible Vessel", the disclosure of which is hereby incorporated byreference. With this alternative nozzle dam unit 152, shown in FIGS. 22,23 and 24, the support structure 154 includes a plurality of lockingpins 156 which are carried in a respective plurality of bosses 158 onthe circumferential periphery at the steam generator side 160 of the damassembly. The pins 156 are adapted to extend radially into acorresponding plurality of holes 162 predrilled in the inner wall 164 ofthe nozzle. FIG. 24 shows one such pin member 156, which is describedmore fully in U.S. Pat. No. 4,770,235, "Nozzle Dam Locking PinAssembly", the disclosure of which is hereby incorporated by reference.The actuation of these preloaded pins can be controlled throughhydraulic connectors associated with the jaw means of the manipulator(See FIG. 25).

FIG. 25 is a block diagram schematic of the auxiliary equipmentassociated with a complete system in accordance with the preferredembodiment. The manipulator is shown having a pedestal section 102 ofthe rotatable base 82 for attachment to the tube sheet 20. The arm 168is shown in alignment with the nozzle dam assembly, to illustrate thatthe wrist or jaw assembly 94 may have associated therewith, pneumatic orhydraulic couplings 170, 172 for direct engagement with respectivemating connectors 174, 176 carried by the nozzle dam assembly 124. Avideo camera 178, preferably connected to the manipulator 76, oroptionally, the tube sheet 20, may also be articulated at 180 foroptimum orientation. These structures are all enclosed within the box182 shown in broken lines, to indicate that they are within the steamgenerator head 12 during use of the system.

The manipulator 76 is controlled from outside the steam generator bymeans of a master console 100 and associated hydraulic and pneumaticservo mechanisms 96 which have respective lines 184 to control thevarious articulated joints. The operator controls the articulated masterarm 186 on the control console 100, and the movements thereof areprecisely reproduced, in scale, at the slave manipulator and jaw. Thiscapability is conventionally available with the Titan 7F manipulatorfrom Schilling Development, Inc., and other vendors.

The pedestal 102 has a similar, but much simpler control system, bywhich a plurality of fingers 188 project from the pedestal and, at theappropriate time, are expanded into the selected tubes of the tubesheet, when an operator throws switches or the like at the interface190, thereby hydraulically or pneumatically delivering, through actuatorbox 192, a flow or pressure through line 194.

A video monitor 196 and a video position controller 198 are respectivelyconnected to the video camera and the positioning servo 200 associatedtherewith.

Another interface 202, in the form of switches or the like, is similarlyconnected to a hydraulic or pneumatic actuator box 204, for actuatinglocking bolts 136 or pins 156, or the like on the nozzle dam assembly152 through the couplings 170, 172, 174, 176 at the manipulator wrist.The interface 202 and hydraulic and pneumatic actuator box 204 could beintegrated with the main manipulator control system 180, 182, 184.

Finally, an independent source 206 of pneumatic pressure and, ifdesired, a leak detection line 208, are connected to the seal portion 34of the dam assembly, in a manner shown in, for example, FIG. 2, and inU.S. Pat. No. 4,482,076.

After the dam has been installed as a dam unit 26 in the nozzle 16, themanipulator 76 would typically be dismounted and removed from the headregion 12 so that inspection repair and other operations can beperformed unimpeded. The lines 48, 208 to the nozzle dam unit 26 would,however, be maintained continuously, for safety and monitoring purposes.

It should thus be appreciated that the method and system describedherein are well adapted to accomplish the objective of remotelyinstalling and removing a nozzle dam. Variations of the particularcomponents and equipment described herein may be substituted withoutdeparting from the scope of the invention as set forth in the claims.

We claim:
 1. A method for remotely installing a nozzle dam in a nuclearsteam generator having a head including a head internal surface, amanway penetrating the head, and a nozzle penetrating the head,comprising the steps of:passing a manipulator through the manway andattaching the manipulator to a head internal surface, the manipulatorhaving a clamp member adapted to be moved within the head while themanipulator is attached to the head; passing a first dam segment throughthe manway and grasping the first segment with the clamp member; whilethe clamp member holds the first dam segment in the vicinity of themanway, attaching at least a second dam segment to the first dam segmentto form a dam subassembly; moving the clamp member with dam subassemblythereon, from the vicinity of the manway through the head to a deployedposition within the nozzle.
 2. The method of claim 1, wherein the stepof attaching a second dam segment to the first dam segment includessliding a male formation on one segment along a female formation on theother segment and locking the segments together.
 3. A method forremotely installing a dam unit in a nozzle or a nuclear steam generatorhead, the head including a manway, comprising the steps of:(a) mountingan articulated manipulator to an internal surface of the head, themanipulator having a free end which carries a jaw member; (b)positioning the manipulator so that the jaw member is adjacent themanway and substantially on the manway axis; (c) passing a first damsegment through the manway and attaching the jaw member to the firstsegment; (d) positioning the manipulator so that the jaw member holdsthe first dam segment on one side of the manway axis; (e) passing asecond dam segment through the manway into engagement with the first damsegment to form a dam subassembly; (f) translating the manipulatorthrough the head until the dam subassembly is adjacent the nozzle; (g)advancing the jaw member toward the nozzle until the cam subassembly ispositioned substantially at the desired location of the dam unit withrespect to the nozzle; and (h) deploying the manipulator to install damsupport structure between the dam subassembly and the steam generator,thereby forming an installed dam unit.
 4. The method of claim 3, whereinthe step of mounting the manipulator includes,passing the manipulatorthrough the manway into the head, supporting the manipulator in the headby a temporary bracing member associated with the manway, and attachinga portion of the manipulator remote from the free end, to supportstructure that is located inside the head.
 5. The method of claim 3,wherein the head includes a tube sheet and the step of mounting themanipulator includes the step of securing the manipulator to the tubesheet of the steam generator.
 6. The method of claim 3, wherein the stepof engaging the second dam segment to the first dam segmentincludes,controlling the jaw member so that a longitudinal edge of thefirst segment is oriented substantially parallel to the manway axis, andmanually interengaging a longitudinal mating edge or the second segmentwith said longitudinal edge in the first segment.
 7. The method of claim3, wherein the dam subassembly is substantially bowl shaped with acircular rim, is constituted from at least three dam segments, andwherein the steps (d) and (e) are repeated with successive dam segmentsuntil the subassembly is completed.
 8. The method of claim 7, whereinthe step of engaging the second dam segment to the first dam segmentincludes interengaging an edge of the second segment with a mating edgeof the first segment, said edges having a longitudinal dimension that isoriented substantially parallel to a diameter of the subassembly.
 9. Themethod of claim 3, wherein the step of installing the dam supportstructure includes,positioning the jaw member adjacent the manway tograsp a support bar, positioning the jaw member within the head so thatthe support bar spans the nozzle opening and interacts with the damsubassembly, and controlling the jaw member to attach the support bar tothe inner wall of the head.
 10. The method of claim 3, wherein thenozzle includes a plurality of radially directed mounting holes and thedam subassembly includes a plurality of fixture means adapted to engagethe mounting holes, and wherein the step of installing the dam supportstructure includes controlling the manipulator to actuate the fixturemeans into engagement with the mounting holes.